However, Putnam says the percentage of "nones" has now skyrocketed to between 30 percent and 40 percent among younger Americans.

Putnam calls this a "stunning development." He gave reporters a first glimpse of his data Tuesday at a conference on religion organized by the Pew Forum on Faith in Public Life.

The research will be included in a forthcoming book, called "American Grace."

This trend started in the 1990s and continues through today. It includes people in both Generation X and Y.

While these young "nones" may not belong to a church, they are not necessarily atheists.

"Many of them are people who would otherwise be in church," Putnam said. "They have the same attitidues and values as people who are in church, but they grew up in a period in which being religious meant being politically conservative, especially on social issues."

Putnam says that in the past two decades, many young people began to view organized religion as a source of "intolerance and rigidity and doctrinaire political views," and therefore stopped going to church.

This movement away from organized religion, says Putnam, may have enormous consequences for American culture and politics for years to come.

"That is the future of America," he says. "Their views and their habits religiously are going to persist and have a huge effect on the future."

Research Finds Churchgoers More Likely to Vote

Putnam, author of the book "Bowling Alone," which tracked the decline in civic and community engagement in America (exemplified by the diminution of bowling leagues), fears the reduction in religiosity could have widespread negative impacts.

His research shows that people who go to church are much more likely to vote, volunteer and give to charity.

However, he says, it's possible that the current spike in young people opting out of organized religion could also prove to be an opportunity for some.

"America historically has been a very inventive and even entrepreneurial place in terms of religion," he says. "We're all the time inventing new religions and reinventing religions that we have. It's partly because we have a free market in religion. That is, we don't have a state church."

Given that today's young "nones" probably would be in church if they didn't associate religion with far-right political views, he says, new faith groups may evolve to serve them.

"Jesus said, 'Be fishers of men,'" says Putnam, "and there's this pool with a lot of fish in it and no fishermen right now."

In the end, he says, this "stunning" trend of young people becoming less religious could lead to America's next great burst of religious innovation.